Lacustrine Cretaceous sequence and climate signal revealed by the Chinese scientific drilling project-SK-I

Lacustrine climate signal is a part of the global environmental and climatic change records. As a paradigm of greenhouse climate in the geological history, the Cretaceous is a particular period. The SK-I drilling located in the northern part of Songliao Basin, NE China and completed in 2007 is supposed to be a breakthrough in this research. The deep core of 2485.89 m with a high recovery ratio of 96.46% has been obtained from SK-I. It presents a continuous Cretaceous lacustrine sequence and provides useful material for Cretaceous research. The sequence of the core reveals uppermost Lower and Upper Cretaceous strata consisting mainly of lacustrine sandstone, dark mudstone, shale, and oilshale. It has been subdivided into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai, and Mingshui formations in ascending order. With the complete core samples, various investigations are carrying out. The Songliao Basin yields the Songhuajiang and Minshui biotas, which avoid direct correlating with marine sequences as strong endemic features.
Based on the study of microfossils, the recent study has recognized certain fossil assemblages in the basin. According to new data of biotic evolutionary stages, lithostratigraphy, chronostratigraphy, chemostratigraphy, seismic stratigraphy and magnetostratigraphy, a preliminary correlation with marine standard sequence has been proposed. The Quantou Formation corresponds to upper Albian-lower Cenomanian stages; Qingshankou Formation correlates to later Cenomanian"CTuronian; Yaojia Formation to Coniacian"CSantonian; Nenjiang Formation to Campanian; and Sifangtai and Minshui Formations to Maastrichtian. We have the possibility to study terrestrial paleontological and sedimentary responses to the Cretaceous major geological events and climate change among other scientific issues. Dominant oilshale bed develops in the Member 1 of Qingshankou Formation and the Members 1-2 of Nenjiang Formation. The formations are major source rocks of the Daqing Oilfield. They are characterized by high TOC and possibly related to the deposits of greenhouse anoxia of mid-Cretaceous. After detailed research the deep core will potentially provide profiles of sedimentology, organic geochemistry, cyclostratigraphy, paleolimnology, geomicrobiology and reconstruction of pCO2. More significant contribution is to get records with a resolution of ten thousand year by the centimeter-grade sampling and analysis. For up to date results, we wish to share the core materials with worldwide scientists and make joint research programs under international cooperation. This work was supported by the National Basic Research Program of China (No. 2006CB701400), the National Natural Science Foundation of China (Grant No. 40672020)